624 Combination of Diagrams. primarily the base line should be volumetric, so in representing these diagrams to the same scale, the bases must be altered to suit the volume of each cylinder respectively, and one pressure scale be used throughout; we shall then see at a glance the comparative work performed in each cylinder, and shall further be able to judge how nearly the total diagram corresponds with what should take place were the whole expansion to occur in one cylinder under theoretically good conditions. Strokes being equal, the area, or diameter squared, will represent cylinder volume. The squares of the diameters are as 4 . 10*89 : 29*2. Taking clearance at \ cylinder volume for the H. P., -fa for the I. P., and -^ for the L. P., they are represented by -5, 1*1, and 2*65. In the large diagram, set up at MA a scale of absolute pressures per sq. in., and measure volumes along OK to any convenient scale. Thus the dotted rectangles CE, ZH, and QU are obtained, in which the indicator diagrams are to be inserted. Divide DE, GH, and JK, each into 10 parts, and erect vertical lines, upon which pressures are to be placed, as taken from corresponding lines on the diagrams w, x, and Y, being careful to set them up to absolute scale; and the shaded curves are obtained. Next mark point of cut-off B, from which to draw the satura- tion curve. The latter being always shewn in terms of specific volume (see Fig. 608), divide AB into 2*7 parts, or the volume of one pound weight of steam at 165 Ibs. absolute pressure. The method of division is shewn at ML : an inclined line is drawn and 2*7 divisions to any scale placed upon it; then parallel lines to ML will divide the latter proportionately. The volume "41 cub. ft. has thus been found, which being crossed by '35 Ibs. sq. in. minus, gives the new origin for the curve BSR, to be drawn as a hyperbola in the usual graphic manner (Fig. 620). A second curve CTU may be traced by dividing AC into 27 parts andr proceeding as before, the origin being then much nearer o. By stepping the cut-off ML into the whole volume MK, the number of total expansions 13*84 is found, the pound weight of steam occupying at the end of the low-pressure stroke a volume of 13*84 x 2 7 or 37*4 cub. ft. The shaded areas, then, further represent the work done by one Ib. weight of steam, if the base lines be specific volumes, and the pressures taken from the